The invention relates generally to the field of cardiopulmonary resuscitation, artificial ventilation, treatment of various types of shock, and treatment of right ventricular failure. In particular, the present invention in some embodiments relates to devices and methods for increasing blood flow to the thorax, including increasing cardiopulmonary circulation during cardiopulmonary resuscitation procedures. In one aspect, increased blood flow to the thorax is accomplished by electrically stimulating the phrenic nerve. Stimulation of the phrenic nerve may also be used to ventilate a patient.
Worldwide, sudden cardiac arrest is a major cause of death and is the result of a variety of circumstances, including heart disease and significant trauma. In the event of a cardiac arrest, several measures have been deemed to be essential in order to improve a patient""s chance of survival. These measures must be taken as soon as possible to at least partially restore the patient""s respiration and blood circulation. One common technique, developed approximately 30 years ago, is an external chest compression technique generally referred to as cardiopulmonary resuscitation (CPR). CPR techniques have remained largely unchanged over the past two decades. With traditional CPR, pressure is applied to a patient""s chest to increase intrathoracic pressure. An increase in intrathoracic pressure induces blood movement from the region of the heart and lungs towards the peripheral arteries. Such pressure partially restores the patient""s circulation.
Traditional CPR is performed by active compression of the chest by direct application of an external pressure to the chest. This phase of CPR is typically referred to as the compression phase. After active compression, the chest is allowed to expand by its natural elasticity which causes expansion of the patient""s chest wall. This phase is often referred to as the relaxation or decompression phase. Such expansion of the chest allows some blood to enter the cardiac chambers of the heart. The procedure as described, however, is insufficient to ventilate the patient. Consequently, conventional CPR also requires periodic ventilation of the patient. This is commonly accomplished by a mouth-to-mouth technique or by using positive pressure devices, such as a self-inflating bag which delivers air through a mask, an endotracheal tube, or other artificial airway.
In order to increase cardiopulmonary circulation induced by chest compression, a technique referred to as active compression-decompression (ACD) has been developed. According to ACD techniques, the active compression phase of traditional CPR is enhanced by pressing an applicator body against the patient""s chest to compress the chest. Such an applicator body is able to distribute an applied force substantially evenly over a portion of the patient""s chest. More importantly, however, the applicator body is sealed against the patient""s chest so that it may be lifted to actively expand the patient""s chest during the relaxation or decompression phase. The resultant negative intrathoracic pressure induces venous blood to flow into the heart and lungs from the peripheral venous vasculature of the patient. Devices and methods for performing ACD to the patient are described in U.S. Pat. Nos. 5,454,779 and 5,645,552, the complete disclosures of which are herein incorporated by reference.
Another successful technique for increasing cardiopulmonary circulation is by impeding air flow into a patient""s lungs during the relaxation or decompression phase. By impeding the air flow during the relaxation or decompression phase, the magnitude and duration of negative intrathoracic pressure is increased. In this way, the amount of blood flow into the heart and lungs is increased. This creates a vacuum in the chest. As a result, cardiopulmonary circulation is increased. Devices and methods for impeding or occluding the patient""s airway during the relaxation or decompression phase are described in U.S. Pat. Nos. 5,551,420 and 5,692,498 and co-pending U.S. application Ser. No. 08/950,702, filed Oct. 15, 1997, now U.S. Pat. No. 6,062,219. The complete disclosures of all these references are herein incorporated by reference.
The above techniques have proven to be extremely useful in enhancing traditional CPR procedures. As such, it would be desirable to provide still further techniques to enhance venous blood flow into the heart and lungs of a patient from the peripheral venous vasculature during both conventional and alternative CPR techniques. It would be particularly desirable to provide techniques which would enhance oxygenation and increase the total blood return to the chest during the relaxation or decompression phase of CPR.
In additional to CPR techniques, other situations exist where blood flow to the thorax is important. Hence, the invention is also related to techniques for returning blood to the thorax for other reasons, i.e., for treating various types of shock, right ventricular failure, post resuscitation pulseless electrical activity, and the like. The invention is also related to providing novel techniques to ventilate a patient, especially in cases where intubation is undesirable or where ventilation can result in the bursting of pulmonary alveoli and bronchioles.
In certain embodiments, the invention provides methods and devices for increasing cardiopulmonary circulation when performing cardiopulmonary resuscitation. The methods and devices may be used in connection with most generally accepted CPR methods. In one exemplary method, a patient""s chest is actively compressed during the compression phase of CPR. At least some of the respiratory muscles, and particularly the inspiratory muscles, are then stimulated to contract during the relaxation or decompression phase to increase the magnitude and prolong the duration of negative intrathoracic pressure during the relaxation or decompression phase, i.e., respiratory muscle stimulation increases the duration and degree that the intrathoracic pressure is below or negative with respect to the pressure in the peripheral venous vasculature. By enhancing the amount of venous blood flow to the heart and lungs, cardiopulmonary circulation is increased.
Among the respiratory muscles that may be stimulated to contract are the diaphragm and the chest wall muscles, including the intercostal muscles. The respiratory muscles may be stimulated to contract in a variety of ways. For example, the diaphragm may be stimulated to contract by supplying electrical current or a magnetic field to various nerves or muscle bundles which when stimulated cause the diaphragm to contract. Similar techniques may be used to stimulate the chest wall muscles to contract. A variety of pulse trains, pulse widths, pulse frequencies and pulse waveforms may be used for stimulation. Further, the electrode location and timing of pulse delivery may be varied. In one particular aspect, an electrical current gradient or a magnetic field is provided to directly or indirectly stimulate the phrenic nerve.
To electrically stimulate the inspiratory motor nerves, electrodes are preferably placed on the lateral surface of the neck over the point where the phrenic nerve, on the chest surface just lateral to the lower sternum to deliver current to the phrenic nerves just as they enter the diaphragm, on the upper chest just anterior to the axillae to stimulate the thoracic nerves, in the oral pharyngeal region of the throat, or on the larynx itself. However, it will be appreciated that other electrode sites may be employed. For example, in one embodiment the respiratory muscles are stimulated by a transcutaneous electrical impulse delivered along the lower antero-lat margin of the rib cage. In one embodiment, inspiration is induced by stimulating inspiratory muscles using one or more electrodes attached to an endotracheal tube or pharyngeal tube.
A variety of other techniques may be applied to further enhance the amount of venous blood flow into the heart and lungs during the chest relaxation or decompression phase of CPR. For example, the chest may be actively lifted during the relaxation or decompression phase to increase the amount and extent of negative intrathoracic pressure. Alternatively, the chest may be compressed by a circumferential binder. Upon release, the chest recoil enhances venous return. During interposed counterpulsation CPR, pressing on the abdomen in an alternating fashion with chest compression also enhances blood return to the heart. In another technique, air flow to the lungs may be periodically occluded during at least a portion of the relaxation or decompression phase. Such occlusion may be accomplished by placing an impedance valve into the patient""s airway, with the impedance valve being set to open after experiencing a predetermined threshold negative intrathoracic pressure.
In one particular aspect of the method, respiratory gases are periodically supplied to the patient""s lungs to ventilate the patient. In another aspect, a metronome is provided to assist the rescuer in performing regular chest compressions.
In still another aspect, the respiratory muscles are stimulated only during certain relaxation or decompression phases, such as every second or third relaxation or decompression phase. In yet another aspect, a defibrillation shock is periodically delivered to the patient to shock the heart or an electrical impulse is delivered to periodically initiate transthoracic pacing.
The invention further provides an exemplary device to assist in the performance of a cardiopulmonary resuscitation procedure. The device comprises a compression member which is preferably placed over the sternum and manually or mechanically pressed to compress the chest. At least one electrode is coupled to the compression member in a way such that the electrode will be positioned to supply electrical stimulation to the respiratory muscles to cause the respiratory muscles to contract following compression of the chest.
In one preferable aspect, a pair of arms extend from the compression member, with one or more electrodes being coupled to the end of each arm. Preferably, the arms are fashioned so as to be adapted to be received over the lower rib cage when the compression member is over the sternum. In this way, the electrodes are placed in a preferred location to stimulate the respiratory muscles to contract. Conveniently, the arms may be fashioned of a flexible fabric so that the arms will conform to the shape of the chest, thereby facilitating proper placement of the electrodes. In one preferable aspect, the electrodes comprise adhesive electrically active pads.
In one particular aspect, a voltage controller or a potentiometer is provided to control the stimulation voltage delivered to the electrode. In this way, a rescuer or a closed loop feedback system may change the voltage output of the electrode to ensure adequate respiratory muscle stimulation. A metronome may optionally be provided and incorporated into the device to assist a rescuer in performing regular chest compressions with the compression member. In another aspect, the stimulation sites may be varied on a periodic basis with an automatic switching box to avoid respiratory muscle or chest wall muscle fatigue.
In one particularly preferable aspect, a pressure or force sensor is disposed in the compression member to sense when a compressive force is being applied to the compression member. Control circuitry may also provided to cause actuation of the electrode when the sensor senses an external compression that is being applied to the compressive member. In this way, a sensor-directed electrical impulse may be emitted from the electrode to transcutaneously stimulate the respiratory muscles to contract at the end of the compression phase. Endotracheal stimulation of respiration muscles is also possible in a similar manner. In cases where a significant delay occurs between delivery of the stimulant and full respiratory muscle contraction, the sensor may be employed to sense when mid-compression (or some other point in the compression phase) occurs to initiate respiratory muscle stimulation sometime before the start of the relaxation or decompression phase.
In still another aspect, a power source is coupled to the electrode. The power source may be integrally formed within the device or may be a separate power source which is coupled to the electrode. As another alternative, the electrode may be coupled to a defibrillator to provide a defibrillation shock or to initiate trans-thoracic cardiac pacing. In another aspect, the voltage controller and power source may be part of a sensor-compression-stimulation device or coupled to the device but separated from the compression-sensor-stimulation device. In still another alternative, the device may be coupled to a ventilator to periodically ventilate the patient based on the number of compressions. In another aspect, impedance or electrical impulses generated by chest compression may be sensed and used by a remote power source and pacer-defibrillation unit to stimulate respiratory muscle contraction using the same sensing electrode(s) or other means to also stimulate the respiratory muscles to contract.
The invention further provides an exemplary device to assist in the performance of cardiopulmonary resuscitation by stimulating the phrenic nerve to cause the diaphragm and/or other respiratory muscles to contract during the relaxation or decompression phase of CPR. Such stimulation may be accomplished by delivering either electrical or magnetic energy to the phrenic nerve. In one embodiment, the phrenic nerve stimulators may be coupled to a chest compression sensor to coordinate chest compressions with the electric or magnetic stimulation of the phrenic nerve. In another aspect, a signal, such as an audible signal or blinking light, may be produced each time electrical inspiration occurs, and manual chest compression is timed based on the emitted signal.
In another embodiment, the device comprises a ventilation member which is coupled to the patient""s airway to assist in the flow of respiratory gases into the patient""s lungs. A sensor may be coupled to the ventilation member to induce application of an electrical current to the phrenic nerve to cause the diaphragm or other respiratory muscles to contract. In this way, a ventilation member which is typically employed to provide ventilation to a patient during a CPR procedure may also function as a stimulant to cause contraction of the diaphragm or other respiratory muscles during the relaxation or decompression phase of CPR. In this manner, the amount of venous blood flowing to the heart and lungs will be enhanced.
A variety of ventilation members may be employed, including endotracheal tubes, laryngeal mask airways, or other ventilation devices which are placed within the larynx, esophagus, or trachea. In one particularly preferable aspect, a pair of electrodes is coupled to the ventilation member so that the device may operate in a unipolar or multipolar manner to stimulate the phrenic nerve. Other aspects include transcutaneous phrenic nerve stimulation with a collar-like device placed around the neck which includes one or more electrodes located on both anterior and posterior surfaces to stimulate the phrenic nerve.
In another embodiment, a system is provided to produce a cough. The system comprises at least one electrode that is adapted to be positioned on a patient to stimulate the abdominal muscles to contract. A valve is also provided and has an open position and a closed position. A controller is coupled to the electrode and the valve and is configured to open the valve after the electrode is actuated to cause the patient to cough,. i.e. the valve allows pressure to build, then opens to release pressure and enhance expiratory gas flow rate similar to a cough. In one aspect, the controller is configured to open the valve for a time in the range from about 10 ms to about 500 ms after the abdominal muscles are stimulated to contract.
The invention further provides an exemplary method for increasing cardiopulmonary circulation when performing cardiopulmonary resuscitation on a patient in cardiac arrest. According to the method, at least some of the abdominal muscles are periodically stimulated to contract sufficient to enhance the amount of venous blood flow into the heart and lungs. In one aspect, the abdominal muscles may be electrically stimulated to contract while preventing respiratory gases from exiting the lungs, and then permitting respiratory gases from exiting the lungs to produce a cough. In another aspect, the patient""s chest is actively compressed during a compression phase and the patient""s chest is permitted to rise during a decompression phase. Further, the abdominal muscles are stimulated to contract during a time period which ranges between a latter portion of the decompression phase to a mid portion of the compression phase.
In another embodiment, a method is provided for increasing blood flow to the thorax of a patient. According to the method, the phrenic nerve is periodically stimulated to cause the diaphragm to contract and thereby causing an increase in the magnitude and duration of negative intrathoracic pressure. This results in a xe2x80x9cgaspxe2x80x9d creating a vacuum, thereby sucking more air and blood into the thorax. Further, when airflow is periodically occluded from flowing to the lungs during contraction of the diaphragm with a valve that is positioned to control airflow into the patient""s airway, the magnitude and duration of negative intrathoracic pressure is further increased to force more blood into the thorax.
In one particular aspect, the phrenic nerve is stimulated by applying electrical current to the phrenic nerve with electrodes that are positioned over the cervical vertebrae between C3 and C7. More preferably, the electrodes are placed both posterior and anterior between C3 and C5. In another aspect, the electrical current is provided in multiphasic form. For example, the wave form may be biphasic, including asymmetrical biphasic. Depending on the particular treatment, the electrical signal may be within certain current ranges, certain frequency ranges, and certain pulse width ranges. Merely by way of example, biphasic electrical current may be used that is in the range from about 100 milliamps to about 2,000 milliamps at a frequency in the range from about 10 Hz to about 100 Hz, and in pulse widths in the range from about 1 xcexcs to about 5 ms.
The methods of the invention may also be used to treat a wide variety of conditions, including for example, hemorrhagic shock, hypovolemic shock, cardiogenic shock, post resuscitation pulseless electrical activity, right ventricular failure, and the like. For instance, when the patient is suffering from hemorrhagic shock, the phrenic nerve may be stimulated about 5 to about 30 times per minute. Further, the phrenic nerve may be stimulated after each breath for time intervals of about 0.25 seconds to about 5 seconds, or in the range from about twice per every one breath to about once about every five breaths. For hypovolemic shock, the phrenic nerve may be stimulated about 5 to about 40 times per minute. When suffering from cardiogenic shock, the phrenic nerve may be stimulated about 5 to about 80 times per minute.
In some cases, the patient may be suffering from cardiac arrest, and the phrenic nerve may be stimulated about 10 to about 100 times per minute in combination with chest compressions that are performed at a rate in the range from about 50 compressions to about 100 compressions per minute. In one option, the chest compressions may be sensed and used to control the timing of phrenic nerve stimulations. Alternatively, a repeating audio and/or visual signal may be provided to indicate to a rescuer when to perform the chest compressions based on the timing of phrenic nerve stimulation. Such a process is described in greater detail in copending U.S. patent application Ser. No. 09/532,601, filed on the same date as the present application, the complete disclosure of which is herein incorporated by reference. In another option, the number of chest compressions relative to the number of phrenic nerve stimulations may be counted.
For patients suffering from post resuscitation pulseless electrical activity, the phrenic nerve may be stimulated about 5 to about 60 times per minute. When suffering from right ventricular failure, the phrenic nerve may be stimulated about 5 to about 80 times per minute. The duration of the stimulation may last from 0.25 to about 6 seconds.
In another embodiment, a method is provided for ventilating a patient, such as when the patient is suffering from respiratory distress or apnea. According to the method, electrodes are placed posterior and anterior on the cervical vertebrae, such as in the C3 to C5 region. Electrical current having a multiphasic waveform, such as an asymmetric biphasic waveform, is supplied to the electrodes to stimulate the phrenic nerve, thereby causing the diaphragm to contract and draw respiratory gases into the patient""s lungs. Conveniently, the phrenic nerve may be stimulated about 3 to about 30 times per minute.
In still another embodiment, a method is provided for increasing blood flow to the thorax of a patient by repeatedly electrically stimulating the diaphragm to contract with at least two electrodes. The magnitude of negative intrathoracic pressure is sensed after diaphragmatic stimulation, and the amount of current that is supplied to the electrode is controlled based on the measured pressure. For example, the sensed measurement may be used to continually adjust the current level so that the magnitude of negative intrathoracic pressure is within the range from about xe2x88x925 mmHg to about xe2x88x9230 mmHg during diaphragmatic stimulation.
In another embodiment, a stimulation device is provided that comprises a generally flat back plate that is configured to be placed below a patient""s back when the patient is lying down. A neck support is coupled to the back plate and serves to tilt the patient""s head backward. Further, at least two electrodes are coupled to the stimulation device to electrically stimulate the patient. For example, the electrodes may be employed to electrically stimulate the phrenic nerve in a manner similar to other embodiments described herein. Optionally, a pair of defibrillation electrodes may also be coupled to the stimulation device to permit a defibrillating shock to be applied.